During loading of the die bores by suitable loadings means the lower plunger of each pair of plungers forms the bottom of a diecavity, with its extent in the die bore providing the desired metering of the powdery or particulate material. The opposite plungers of each pair of plungers are moved towards each other at a compression station so as to compress the powdery or particulate material to obtain tablets or pellets of a desired thickness. The compression station generally includes precompression and main compression means. After the compression operation, the lower plungers as controlled by an injection cam eject the tablets or pellets from the die bores at a predetermined location of the pressing machine while the upper plungers progressively move away from the die rotor. This allows a stripper to strip off the ejected pressed articles from the die rotor and to feed them to a discharge path.
It is necessary to inspect among other properties the weight of the tablets manufactured in this manner and eventually to provide for correction of the weight if it is not within desired limits. To this end the discharge path may include switch means for selectively branching off the tablets towards an inspection station. Inspection stations which automatically perform inspection procedures are also known.
Tablets or pellets that are made up of two-layers may be manufactured by means of a twin rotor pressing machine of the above-identified type wherein the described stations are provided two-fold. Initially, powdery or particulate material is loaded within the die bores and are slightly precompressed so as to form first layers. Thereafter, powdery or particulate material is loaded onto said first layers so as to form second layers thereon. The first and second layers are compressed so as to form two-layer tablets or pellets which are removed in the above described manner. If the inspection indicates that the actual weight of the two-layer tablets or pellets deviates from a desired value, it is not recognizable whether it is the first, the second, and/or both layers that are faulty. Accordingly, it is necessary to inspect the weight also of the first layers. In the past, this has been done manually. The first layers are removed manually, and the loading means arranged upstream of said second compression station has made been inoperative and has been moved away from the die rotor by hydraulic actuation means.
The prior art method does not enable completely automatic operation but rather requires manual operation at least for drawing samples of the first layers. Another drawback of the prior art method is that uncompressed powdery or particulate material may collect on the disk-shaped die rotor and the adjacent areas of the pressing machine. Loss of material and/or intermixing of the first layer material and the second layer material may result therefrom. Further, repeated cleaning of the pressing machine is required.